Magnetic random access memory and method of manufacturing the same

ABSTRACT

A write wiring for writing information in an MTJ device is covered with a magnetic layer. The magnetic layer has a structure in which the growing direction of columnar grains is 300 or less from the normal-line direction of sidewalls, a structure in which grains are deposited like a layer, or a structure in which grains are amorphously deposited.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2003-065055, filed Mar. 11,2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic random access memory (MRAM).Moreover, the present invention relates to a structure of a write wiringfor writing data in a memory cell of the MRAM.

2. Description of the Related Art

Many memories for storing information in accordance with a new principlehave been proposed in recent years. As one of the memories, anonvolatile and high-speed MRAM in which magnetic memory cellsconstituted by an MTJ (Magnetic Tunnel Junction) device for storinginformation of “0” and “1” in accordance with the tunneling magnetoresistive effect are arranged like a matrix is described in, forexample, Roy Scheuerlein et. al “A 10-ns Read and Write Non-VolatileMemory Array Using a Magnetic Tunnel Junction and FET Switch in-eachCell”, ISSCC 2000 Technical Digest pp. 128-129.

Data is written in an MTJ device by supplying a current to a write wordline and a bit line and making the spin direction of the MTJ deviceparallel or antiparallel by using a magnetic field generated by thecurrent circulating through the both lines.

It is said that the largest problem of an MRAM is reduction of a writecurrent. An MTJ device reported at present requires a large writecurrent value of 8 to 10 mA when the cell width ranges between 0.4 and0.6 μm and the cell length is approx. 1.2 μm. Therefore, the MTJ devicehas a problem on electromigration of a wiring and a problem that adriving circuit occupies a large area.

Even in the case of a test chip of a 1K-bit-level MRAM fabricated by thepresent inventors by way of trial, a write current also ranges between 8and 10 mA. To practically use the MRAM, it is indispensable to reducethe write current value to an allowable level such as 1 to 2 mA.

To rewrite data in an MTJ device, it is necessary to invert themagnetizing direction of a recording layer of the MTJ device. Aswitching field Hsw necessary to rewrite the magnetization informationof the recording layer is approximately obtained from the followingexpression:Hsw=4π×Ms×t/F (Oe)where Ms denotes saturated magnetization of the recording layer, tdenotes a thickness of the recording layer, and F denotes a width of therecording layer.

Reduction of the thickness of the recording layer of an MTJ device isrestricted to secure the stability of the information. In the case of anMTJ device in which the width F of the recording layer is decreased toapprox. 0.15 μm or less, it is necessary to increase the thickness t ofthe recording layer.

Even if forming the recording layer by a CoFeNi thin film and settingthe thickness of the layer to 2 nm, the switching filed Hsw isintensified and a write current further increases by decreasing thewidth F of the recording layer and fining the MTJ device.

On the other hand, a current density to be supplied to a wiring has anupper limit. In the case of a copper wiring, the upper limit is approx.10⁷ A/cm². Because the sectional area of the wiring decreases as thedevice is further fined, it is impossible to supply a current capable ofgenerating the switching field Hsw necessary to invert the magnetizationof the recording layer.

As a method for reducing a write current in an MRAM, it is reported in,for example, Saied Tehrani, “Magneto resistive RAM”, 2001 IEDM shortcoursew to use a write wiring provided with a yoke covered with a softmagnetic body made of NiFe or the like for a wiring made of Cu.

As a result of studying a case of using the write wiring provided withthe yoke described in the above document through an experiment and acomputer simulation, an efficient improvement effect of approx. twotimes ca be confirmed and a write current can be decreased to 5 mA.However, a write current of 5 mA is a limit. Therefore, the value 5 mAis far from reduction of current to 1 to 2 mA which is a target value ofa write current necessary for practical use.

Moreover, as a result of quickly writing data at a short-pulse writecurrent of approx. 50 nsec, a necessary write current fluctuates andonly a reproducibility can be obtained which is greatly lower than areproducibility 90% when writing data at a constant write current.

As described above, though a write wiring provided with a yoke isproposed which is obtained by covering the side face of the write wiringwith a magnetic layer in order to reduce the write current of an MRAM,it has a write current considerably larger than a target value necessaryfor practical use. Moreover, as a result of quickly writing data at ashort-pulse write current, problems occur that a necessary write currentvalue fluctuates and write reproducibility is low.

Therefore, it is requested that a write current can be reduced and writereproducibility is secured without fluctuation of a write current valueeven when writing data at a short-pulse write current.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided amagnetic random access memory including: a write wiring constituted byat least one wiring; a magnetic tunnel junction device which is disposedclosely to the write wiring and in which information is written inaccordance with an induced magnetic flux generated by supplying acurrent to the write wiring; and a magnetic layer which is provided soas to cover at least a part of a sidewall of the write wiring and formedby grown columnar grains and in which the growing direction of thecolumnar grains is 30° or less from the normal-line direction of thesidewall.

According to another aspect of the present invention, there is provideda method for manufacturing a magnetic random access memory on asemiconductor substrate, including: forming an insulating film on thesemiconductor substrate; forming a trench in the insulating film; thougha sputtering method for sputtering the magnetic body, depositing amagnetic layer including at least two of the following three types suchas a type having a structure in which the normal-line direction ofcolumnar grains is 30° or less from a sidewall of the trench formed onthe insulating film formed on the semiconductor substrate, a type havinga structure in which grains are deposited like a layer, and a typehaving a structure in which grains are amorphously deposited on thesidewall of the trench; and embedding the write wiring in the trench.

According to still another aspect of the present invention, there isprovided a method for manufacturing a magnetic random access memory on asemiconductor substrate, including: forming an insulating film on thesemiconductor substrate; depositing a wiring material on the insulatinglayer; patterning the wiring material and thereby forming the writewiring; and depositing a magnetic layer including at least two of thefollowing three types such as a type having a structure in which thegrowing-direction angle of columnar grains is 30° or less from thenormal-line direction of a sidewall of the write wiring, a type having astructure in which grains are deposited like a layer, and a type havinga structure in which grains are amorphously deposited on the writewiring through a sputtering method.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view showing a general structure of an MTJ devicefor use in an MRAM;

FIGS. 2A and 2B are views showing spin directions of two magnetic layersof the MTJ device in FIG. 1;

FIG. 3 is an illustration schematically showing a planar layout of acell array of an MRAM;

FIG. 4 is a sectional view showing a structure noticing one memory cellin a plane vertical to a bit line along the line IV-IV in FIG. 3;

FIG. 5 is a sectional-view showing a structure in a plane vertical to awrite word line along the line V-V in FIG. 3;

FIG. 6 is a characteristic diagram showing the characteristic of aresistance-value change according to inversion of an applied magneticfield of the MTJ device shown in FIG. 1;

FIG. 7 is a characteristic diagram showing an asteroid curve of the MTJdevice shown in FIG. 1;

FIG. 8 is a perspective view showing a structure of a yoke-providedwrite wiring;

FIG. 9 is a characteristic diagram schematically showing a state inwhich the write efficiency is improved when writing data by using theyoke-provided write wiring shown in FIG. 8;

FIG. 10 is an illustration schematically showing an arrangement relationbetween an MTJ device and a write wiring according to a first embodimentof an MRAM of the present invention;

FIG. 11 is an illustration schematically showing an arrangement relationbetween an MTJ device and a write wiring according to a secondembodiment of the MRAM of the present invention;

FIG. 12 is a sectional view schematically showing a crystalline state ofa magnetic layer for covering sidewalls of the write wiring in FIGS. 10and 11;

FIGS. 13A to 13C are illustrations schematically showing results ofexamining the crystalline state of the magnetic layer in FIG. 12 throughsectional TEM observation;

FIG. 14 is an illustration showing a relation between an angle θ of thegrowing direction of the columnar grains shown in FIG. 12 and a writecharacteristic when using a write wiring corresponding to the angle θ;

FIG. 15 is a characteristic diagram showing a relation between a writecurrent depending on the difference between methods for forming amagnetic layer of the write wiring in FIGS. 10 and 11 and thereproducibility when writing data by a short-pulse write current;

FIG. 16 is a sectional view showing some of steps according to a firstembodiment of an MRAM manufacturing method of the present invention;

FIG. 17 is a sectional view showing some of steps according to a secondembodiment of the MRAM manufacturing method of the present invention;

FIG. 18 is a sectional view showing some of steps according to a thirdembodiment of the MRAM manufacturing method of the present invention;

FIG. 19 is a sectional view showing some of steps according to a fourthembodiment of the MRAM manufacturing method of the present invention;

FIG. 20 is a sectional view showing some of steps according to a fifthembodiment of the MRAM manufacturing method of the present invention;

FIG. 21 is a sectional view showing some of steps according to a sixthembodiment of the MRAM manufacturing method of the present invention;

FIG. 22 is a block circuit diagram of a DSL data path portion of adigital subscriber line modem as one of application examples of MRAM;

FIG. 23 is a block circuit diagram of a circuit portion for realizingcommunication function in a cellphone terminal as another applicationexample of MRAM;

FIG. 24 is a top view showing an example in which the MRAM is applied toan MRAM card;

FIG. 25 is a top view of a transfer device of card insert type fortransferring data on the MRAM card in FIG. 24;

FIG. 26 is a side view of the transfer device in FIG. 25;

FIG. 27 is a side view of a transfer device of fit-in type fortransferring data on the MRAM card in FIG. 24; and

FIG. 28 is a side view of a transfer device of slide type fortransferring data on the MRAM card in FIG. 24.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention is described below in detail byreferring to the accompanying drawings.

FIG. 1 schematically shows a sectional structure of an MTJ device foruse in an MRAM.

An MTJ device has a structure in which a nonmagnetic layer (tunnelbarrier film) 73 is held by two magnetic layers 71 and 72 respectivelyformed by a ferromagnetic layer or a ferromagnetic body. The MTJ devicehaving the above structure stores information of “0” and “1” dependingon whether the spin directions of the two magnetic layers 71 and 72 areparallel or antiparallel.

An antiferromagnetic layer 74 is normally disposed to either of the twomagnetic layers 71 and 72. The antiferromagnetic layer 74 is a memberfor easily rewriting the information by fixing the spin direction of onemagnetic layer 72 and changing only the spin direction of the othermagnetic layer 71. In this case, the magnetic layer 71 at thevariable-spin side is referred to as a free layer or recording layer andthe magnetic layer 72 at the spin fixed side is referred to as a fixedlayer or pin layer.

FIGS. 2A and 2B show two states of spin directions of two magneticlayers 71 and 72 of the MTJ device shown in FIG. 1.

As shown in FIG. 2A, when spin directions (directions shown by arrows)of the magnetic layers 71 and 72 are parallel, that is, the same, thetunnel resistance of the tunnel barrier film 73 held by the magneticlayers 71 and 72 is minimized. That is, the tunnel current is maximized.

As shown in FIG. 2B, when spin directions of the magnetic layers 71 and72 are antiparallel each other, the tunnel resistance of the tunnelbarrier film 73 held by the magnetic layers 71 and 72 is maximized, thatis, the tunnel current is minimized.

In the case of an MRAM, two states in which resistance values of an MTJdevice are different from each other are made to correspond to aninformation-“1” storing state (state “1”) and an information-“0” storingstate (state “0”).

FIG. 3 schematically shows a planar layout of a cell array of an MRAM.

A plurality of write/read bit lines BL and a plurality of write wordlines WWL are arranged so as to be orthogonal each other and an MTJdevice having the structure shown in FIG. 1 is disposed closely to thebit lines BL and write word lines WWL correspondingly to each ofintersections between the bit lines BL and the write word lines WWL.Each MTJ device is set such that the major side of a rectangle isparallel with the write word lines WWL and the minor side of therectangle is parallel with the bit lines BL. Moreover, a spin directionis provided so as to be parallel with the major-side direction. Each bitline BL is electrically connected to each of the fixed layers of the MTJdevices in the same row or column. Each write word line WWL is set so asto closely face each of the MTJ devices in the same column or row.

FIGS. 4 and 5 show sectional structures in different directions of oneMTJ device in FIG. 3. In FIGS. 4 and 5, reference numeral 10 denotes asemiconductor substrate formed by a P-type Si substrate, 11 denotes ashallow-trench-type isolation region (STI), 12 denotes a gate oxidefilm, 13 denotes an impurity diffusion layer (N⁺) serving as a drainregion or source region of read-cell selecting transistor (NMOSFET), 14denotes a gate electrode (GC), 15 denotes a first metal wiring layer(M1), 16 denotes a second metal wiring layer (M2), 17 denotes an MTJconnecting wiring formed by a third metal wiring layer (M3), 18 denotesa conductive contact plug for electrically connecting the first metalwiring layer 15 to the diffusion layer 13, 19 denotes a conductivecontact plug for electrically connecting the second metal wiring layer16 to the first metal wiring layer 15, 20 denotes a conductive contactplug for electrically connecting the third metal wiring layer 17 to thesecond metal wiring layer 16, 21 denotes an MTJ device, 22 denotes afourth metal wiring layer (M4), 23 denotes a conductive contact plug forelectrically connecting the fourth metal wiring layer 22 to the MTJdevice 21, and 24 denotes a interlayer insulating film.

In FIGS. 4 and 5, as purposes of wirings, BL shows a write/read bitline, WWL shows a write word line, SL shows a source line, and RWL showsa read word line. The source line SL is connected to the groundpotential.

Then, the principle for writing data in an MTJ device is describedbelow.

Data is written in the MTJ device by supplying a current to the writeword line WWL and bit line BL by using magnetic fields generated by thecurrent circulating through the both lines and thereby making spindirections of the MTJ device parallel or antiparallel.

That is, to write information in the MTJ device, a magnetic field Hx isgenerated by supplying a current proceeding to a first direction or asecond direction opposite to the first direction to the bit line BL inaccordance with write data and a magnetic field Hx is generated bysupplying only a current proceeding to a certain direction to the writeword line WWL. Thereby, a resultant magnetic field is generated andinformation is written by using the resultant magnetic field. In thiscase, by supplying the current proceeding to the first direction to thebit line BL, spin directions of the MTJ device becomes parallel.However, when supplying the current proceeding to the second directionto the bit line BL, spin directions of the MTJ device becomeantiparallel.

To read information from the MTJ device, the read word line RWL isactivated and only a switching device connected to the selected MTJdevice is turned on to form a current route. Then, a current is suppliedfrom the selected bit line BL to the ground potential. As a result, acurrent corresponding to the resistance value is supplied to only theselected MTJ device and it is possible to read information by detectingthe current value.

Then, a mechanism in which spin directions of the MTJ device are changedis briefly described below by referring to FIGS. 6 and 7.

FIG. 6 shows a characteristic (MTJ curve) of a resistance-value changedue to inversion of a magnetic field applied to the MTJ device and FIG.7 shows an asteroid curve of the MTJ device.

As shown in FIG. 6, by applying the magnetic field Hx in the easy-axisdirection of the MTJ device, resistance values of the MTJ device arechanged by approx. 17%. A change rate which is a ratio betweenresistances before and after the change is referred to as an MR ratio.The MR ratio depends on the property of a magnetic layer of the MTJdevice. At present, an MTJ device having an MR ratio of approx. 50% isobtained. A resultant magnetic field between the magnetic field Hx inthe easy-axis direction and the magnetic field in the hard-axisdirection is applied to the MTJ device.

As shown by continuous lines and broken lines in FIG. 6, intensities ofthe magnetic field Hx in the easy-axis direction necessary to changeresistance values of the MTJ device are also changed. By using the abovephenomenon, it is possible to write data in only an MTJ device disposedcorrespondingly to the intersection between the selected write word lineWWL and the selected bit line BL among memory cells arranged in an arraymanner.

Namely, as shown in FIG. 7, when the intensity of the resultant magneticfield between the easy-axis-directional magnetic field Hx and thehard-axis-direction magnetic field Hy is present at the outside of theasteroid curve, for example, positions of two black circles in FIG. 7,it is possible to invert the spin direction of the magnetic layer of theMTJ device.

On the contrary, when the magnitude of the resultant magnetic fieldbetween the easy-axis-directional magnetic field Hx and thehard-axis-directional magnetic field Hy is present at the inside of theasteroid curve, for example, positions of two white circles in FIG. 7,it is impossible to invert the spin direction of the magnetic layer ofthe MTJ device.

Therefore, it is possible to control writing data in the MTJ device bychanging the intensity of the resultant magnetic field between theeasy-axis-directional magnetic field Hx and the hard-axis-directionmagnetic field Hy, and by changing positions the intensity of theresultant magnetic field in the Hx-Hy plane.

As described above, it is a largest problem of an MRAM to reduce a writecurrent.

FIG. 8 shows a structure of a yoke-provided-write wiring described SaiedTehrani, “Magneto resistive RAM”, 2001 IEDM short coursew. Moreover,FIG. 9 shows a characteristic for improving a write efficiency whenwriting data by using the write wiring shown in FIG. 8. Thecharacteristic A in FIG. 9 shows a state in which a switching magneticfield Hsw is intensified as the MTJ device is further fined in a case ofusing a CoFeNi thin film having the thickness of 2 nm as the recordinglayer of the MTJ device.

When using a normal write wiring, it is possible to write data becausethe generated magnetic field is stronger than the switching magneticfield until 1/F is approx. 7. On the contrary, when using theyoke-provided write wiring described in Saied Tehrani, “Magnetoresistive RAM”, 2001 IEDM short coursew, it is possible to write databecause the generated magnetic field is stronger than the switchingmagnetic field even if 1/F exceeds approx. 7. However, when 1/F exceedsapprox. 10, the generated magnetic field is weaker than the switchingmagnetic field. That is, it is possible to reduce a write current to 5mA but the value 5 mA is far from 1 to 2 mA which is a target valuenecessary for practical use.

As a result of quickly writing data with a write current of a shortpulse of approx. 50 nsec, a necessary write current fluctuates and onlya reproducibility greatly lower than a reproducibility of 90% whenwriting data with a constant write current can be obtained.

In the case of the MRAM of the present invention, a part of a writewiring is covered with a magnetic layer and there is a feature in thestructure of the magnetic layer. Moreover write wirings respectivelycovered with a magnetic layer include the bit wiring BL and write wordline WWL in FIG. 3.

First Embodiment of MRAM

FIG. 10 schematically shows an arrangement relation between an MTJdevice and a write wiring of a memory cell for use in a first embodimentof the MRAM of the present invention. The write word line (WWL) 16 whichis one of write word lines is disposed below the MTJ device 21. Thebottom face and both sidewalls of the write word line 16 arecontinuously covered with a magnetic layer 25. The bit line (BL) 22disposed on the MTJ device 21 is not covered with a magnetic layer.

Second Embodiment of MRAM

FIG. 11 schematically shows an arrangement relation between an MTJdevice and a write wiring of a memory cell for use in a secondembodiment of the MRAM of the present invention. The bit line (BL) 22which is one of write wirings is disposed on the MTJ device 21. Theupper face and both sidewalls of the bit line 22 are continuouslycovered with the magnetic layer 25. The write word line (WWL) 16disposed below the MTJ device 21 is not covered with a magnetic layer.

In the case of an MRAM having a memory cell of the structure shown inFIG. 10 or 11, information of “0” and “1” are made to correspond to aresistance value to be changed in accordance with a magnetizedarrangement state of two magnetic layers of the MTJ device 21constituted by two magnetic layers holding a nonmagnetic layer.Information is written by supplying a current to the write word line 16or the bit line 22 serving as a write wiring disposed closely to the MTJdevice 21 to generate an induced magnetic field and changing magnetizeddirections of a recording layer of the MTJ device 21. The MTJ device 21is formed on a semiconductor substrate including an SOI (silicon oninsulator) substrate or the like.

In FIGS. 10 and 11, the MTJ device 21 has a structure in which a tunnelbarrier film is held between a recording layer formed by a magneticlayer and a fixed layer similarly to the structure described above byreferring to FIG. 1 and has a magnetoresistive effect. Anantiferromagnetic layer is disposed at the fixed layer side.

The write word line 16 or bit line 22 serving as a write wiring is madeof, for example, Cu and at least one of the sidewalls of the line 16 or22, three faces other than one face opposite to the MTJ device 21 in theabove embodiments are covered with the magnetic layer 25.

FIG. 12 schematically shows a crystalline state of the magnetic layer 25covering sidewalls of the write wirings in FIGS. 10 and 11. In thiscase, a crystalline state of the magnetic layer 25 covering sidewalls ofthe bit line 22 in the structure shown in FIG. 11 is shown as a typicalexample. The magnetic layer 25 has at least one or two structures amonga portion 125 a formed by columnar grains grown from sidewalls of thebit line 22, a portion 25 b having a structure in which grains aredeposited like a layer, in other words, a layer is granularly grown, anda portion 25 c having a structure in which the boundary between grains(grain boundary) is opaquely amorphously deposited.

FIGS. 13A to 13C schematically show results of examining crystallinestates of parts of the magnetic layers 25 a to 25 c shown in FIG. 12through sectional TEM observation.

FIG. 12 and FIGS. 13A to 13C respectively show a case in which the bitline 22 serves as a write wiring. However, the write word line 16 mayserve as a write wiring uses.

The magnetic layer 25 of the above embodiments is different from themagnetic layer shown in FIG. 8 in that the layer 25 is formed by atleast one of the portions such as the portion 25 a having a structure inwhich the growing direction of columnar grains is 30° or less from thenormal-line direction of a sidewall, the portion 25 b having a structurein which grains are deposited like a layer, and the portion 25 c havinga structure in which the boundary between grains is opaquely amorphouslydeposited.

As a result of studying various manufacturing methods for coveringsidewalls of the write wiring with the magnetic layer 25 and forming themagnetic layer 25 through a manufacturing method according to thecondition to be described later, a very preferable result is obtained onreduction of the write current and write reproducibility. A result ofobserving the magnetic layer 25 in detail is described below.

FIG. 14 shows a relation between the angle θ of the growing direction ofcolumnar grains from the normal-line direction of a sidewall shown inFIG. 13A and a write characteristic when using a write wiringcorresponding to the angle θ.

When the angle θ formed between the growing direction of columnar grainsand the normal line of sidewalls of the bit line 22 is 30° or less asshown in FIG. 12, a write current value greatly decreases from 5 mAwhich is a prior limit and write reproducibility becomes approx. 100% ascan be seen from the characteristic shown in FIG. 14. That is, it ispossible to decrease the write current value to less than 5 mA, moreaccurately, to 1 to 2 mA and the write reproducibility at a short pulseof 50 nsec becomes approx. 100%.

As a result of forming the magnetic layer 25 by various manufacturingmethods to be described later and evaluating write characteristics,every characteristic shows a preferable value. As a result of examiningthe morphology of the magnetic layer 25 in the above case throughsectional TEM observation, the following types are found: a type havinga structure in which the angle θ formed between the growing direction ofcolumnar grains of the magnetic layer 25 and the normal line ofsidewalls of the write wiring is 30° or less, a type having a structurein which grains of the magnetic layer 25 are deposited like a-layer, anda type having a structure in which the grain boundary of the magneticlayer 25 is opaquely amorphously deposited.

Namely, in the case of write wirings of the above both embodiments, thecrystalline state of the magnetic layer 25 covered with sidewalls isimproved. That is, by forming the magnetic layer 25 including any one ortwo or more of the following three types such as a type having astructure in which the angle θ formed between the growing direction ofcolumnar grains and the normal line of sidewalls of a writing wiring is30° or less, a type having a structure in which a layer is granularlygrown, that is, grains are deposited like a layer, and a type having astructure in which grains are amorphously deposited, it is possible togreatly reduce a write current and realize reproducible writing.

FIG. 15 shows a relation between a write current depending on thedifference between manufacturing methods to be described later and thereproducibility when writing data with a short-pulse write current ofthe magnetic layer 25 formed on the write word line 16 or bit line 22serving as a write wiring.

For the above embodiments, a case is described in which the magneticlayer 25 is formed on either wiring of the write word line 16 and bitline 22. However, it is also allowed to form the magnetic layer 25 onthe both of the write word line 16 and bit line 22.

First Embodiment of MRAM Manufacturing Method

FIG. 16 schematically shows a first embodiment of an MRAM manufacturingmethod of the present invention. This embodiment uses a sputteringmethod to form a magnetic layer on sidewalls of a write wiring.

In other words, FIG. 16 shows a manufacturing step when forming a writewiring by forming an interlayer insulating film 41 on a semiconductorsubstrate 40 and a trench 42 on the interlayer insulating film 41 andembedding a write wiring material in the trench 42. This step is appliedto a case of forming the write word line 16 serving as a write wiringbelow the MTJ device 21 as sown in FIG. 10.

First, for example, a Ta layer 43 is deposited on sidewalls of thetrench 42 before embedding the write wiring material in the trench 42formed on the interlayer insulating film (such as SiOx film) 41 on thesemiconductor substrate 40. Under the above state, a magnetic body 44made of NiFe or the like is deposited on the bottom face of the trench42 and moreover, the magnetic layer 25 made of NiFe or the like isdeposited such that the growing direction of columnar grains is 30° orless from the normal-line direction of sidewalls of the trench 42 byusing a sputtering method for sputtering the magnetic body 44 with argon(Ar) or the like.

Thereafter, by embedding-a write wiring material, for example, Cu in thetrench 42, the angle of the magnetic layer 25 is 30° or less from thenormal-line direction of sidewalls of the write wiring as shown in FIG.12.

It is also allowed to form sidewalls of the trench 42 almost verticallyto a substrate face or like a taper such that the opening end of thetrench 42 becomes wider than the bottom face thereof.

Second Embodiment of MRAM Manufacturing Method

FIG. 17 schematically shows a second embodiment of the MRAMmanufacturing method of the present invention. This embodiment also usesa sputtering method when forming a magnetic layer on sidewalls of awrite wiring.

That is, FIG. 17 shows a manufacturing step when forming a write wiringby forming an interlayer insulating film 41 on a semiconductor substrate40, depositing a write wiring material on the interlayer insulating film41, and patterning the write wiring material. This step is applied to acase of forming the bit line 22 serving as a write wiring on the MTJdevice 21 as shown in FIG. 11.

First, after depositing a wiring material made of, for example, Cu onthe interlayer insulating film (such as SiOx film) 41, the bit line 22serving as a write wiring is left by patterning the wiring materialthrough RIE (Reactive Ion Etching). Thereafter, a magnetic layer 45 madeof NiFe or the like is deposited on the horizontal plane of thesubstrate and then, a magnetic layer 25 made of NiFe or the like isdeposited such that the growing direction of columnar grains is 30° orless from the normal-line direction of sidewalls of the bit line 22 asshown in FIG. 12 by a sputtering method for sputtering the magnetic body45 with argon (Ar) or the like.

In this case, though there are some magnetic grains directly depositedon sidewalls of the bit line 22 from the cathode electrode of asputtering apparatus, the growing direction of columnar grainsapproaches the normal line of the sidewalls in parallel because of theinfluence of grains deposited from a substrate surface.

Moreover, it is possible to improve the characteristic of the magneticlayer by using the sputtering method in which the flying direction ofmagnetic grains coming from the cathode electrode of the sputteringapparatus becomes vertical to sidewalls of the bit line 22 in the caseof a method for forming a film by tilting the substrate by using IBS(Ion Beam Sputtering) or the like.

Furthermore, it is also effective to apply a bias or ion beam to thesubstrate.

Third Embodiment of MRAM Manufacturing Method

FIG. 18 schematically shows a third embodiment of the MRAM manufacturingmethod of the present invention. This embodiment uses a sputteringmethod for ionizing sputter grains when forming a magnetic layer onsidewalls of a write wiring.

That is, FIG. 18 shows a manufacturing step when forming a write wiringby forming an interlayer insulating film 41 on a semiconductor substrate40, forming a trench 42 on the interlayer insulating film 41, andembedding a write wiring material in the trench 42. This step is used toform the write word line 16 serving as a write wiring below the MTJdevice 21 as shown in FIG. 10.

First, for example, a Ta layer 43 is deposited on sidewalls of thetrench 42 before embedding the write wiring material in the trench 42formed on the interlayer insulating film (such as SiOx film) 41 on thesemiconductor substrate 40. Thereafter, a magnetic body 44 made of NiFeor the like is deposited on the bottom of the trench 42. Then, by flyingions such as Ni⁺, Fe⁺, and NiFe⁺ obtained by ionizing sputter grains ofthe magnetic body made of, for example, NiFe on a substrate surface, amagnetic layer 25 is deposited such that the growing direction ofcolumnar grains is 30° or less from the normal-line direction ofsidewalls of the trench 42. Thereafter, by embedding a write wiringmaterial, for example, Cu in the trench 42, the angle of the magneticlayer 25 becomes 30° or less from the normal-line direction of sidewallsof the write wiring.

By ionizing and flying sputter grains as described above, a phenomenonappears that the growing direction of columnar grains approaches beingparallel with the normal line of sidewalls. Moreover, when an ionizationrate exceeds 20%, the above phenomenon becomes extreme.

As described above, a magnetic layer formed by a sputtering method forionizing sputter grains is improved in write reproducibility compared toa magnetic layer formed by the normal sputtering method.

It is allowed to form sidewalls of the trench 42 to be almost verticalto a substrate surface or like a taper in which opening end of thetrench becomes wider than the bottom face thereof.

Fourth Embodiment of MRAM Manufacturing Method

FIG. 19 schematically shows a fourth embodiment of the MRAMmanufacturing method of the present invention. This embodiment also usesa sputtering method to form a magnetic layer on sidewalls of a writewiring.

That is, FIG. 19 shows a manufacturing step when forming a write wiringby forming an interlayer insulating film 41 on a semiconductor substrate40, depositing a write wiring material on the interlayer insulating film41, and patterning the write wiring material. As shown in FIG. 11, theabove step is applied to form the bit line 22 serving as a write wiringon the MTJ device 21.

First, the bit line 22 serving as a write wiring is left by depositing awiring material made of, for example, Cu on the interlayer insulatingfilm (such as SiOx film) 41 and then patterning the wiring materialthrough RIE (Reactive Ion Etching). Then, a magnetic body 45 made ofNiFe or the like is deposited on the horizontal plane of the substrateto deposit a magnetic layer 25 made of NiFe or the like such that thegrowing direction of columnar grains is 30° or less from the normal-linedirection of sidewalls of the bit line 22 as shown in FIG. 12 by asputtering method for sputtering the magnetic body 45 with argon (Ar) orthe like.

Fifth Embodiment of MRAM Manufacturing Method

FIG. 20 schematically shows a fifth embodiment of the MRAM manufacturingmethod of the present invention. This embodiment uses a plating methodwhen forming a magnetic layer on sidewalls of a write wiring.

That is, FIG. 20 shows a manufacturing step when forming a write wiringby forming an interlayer insulating film 41 on a semiconductor substrate40, forming a trench 42 on the interlayer insulating film 41, andembedding a write wiring material in the trench 42. As shown in FIG. 10,the above step is applied to form the write word line 16 serving as awrite wiring below the MTJ device 21.

First, a barrier metal formed by a Ta film and a plated seed layer 46are deposited on sidewalls of the trench 42 before embedding the writewiring material in the trench 42 formed on the interlayer insulatingfilm (such as SiOx film) 41 on the semiconductor substrate 40. Under theabove state, a magnetic layer 25 is formed such that the growingdirection of columnar grains is 30° or less from the normal-linedirection of sidewalls of the trench by a plating method. Thereafter, byembedding the write wiring in the trench 42, the magnetic layer 25becomes 30° or less from the normal-line direction of sidewalls of thewrite wiring as shown in FIG. 12.

When using NiFe for the plated seed layer 46, the magnetic layer 25 madeof NiFe or the like formed through plating shows a preferable writecharacteristic in a comparatively wide process condition.

Moreover, by using Cu for the plated seed layer and directly plating andgrowing NiFe on Cu, it is possible to control a composition with thewhole plated film, that is, it is possible to avoid an abnormalcomposition of a plated initial layer and a preferable writecharacteristic can be stably obtained.

It is allowed to form sidewalls of the trench 42 almost vertically to asubstrate surface or into a taper such that the opening end of thetrench becomes wider than the bottom face thereof.

Sixth Embodiment of MRAM Manufacturing Method

FIG. 21 schematically shows a sixth embodiment of the MRAM manufacturingmethod of the present invention. This embodiment also uses a platingmethod when forming a magnetic layer on sidewalls of a write wiring.

That is, FIG. 21 shows a manufacturing step when forming a write wiringby forming an interlayer insulating film 41 on a semiconductor substrate40, depositing a write wiring material on the interlayer insulating film41, and patterning the write wiring material. As shown in FIG. 11, theabove step is applied to form the bit line 22 serving as a write wiringon the MTJ device 21.

First, the bit line 22 serving as a writ wiring is left by depositing awiring material made of, for example, Cu on the interlayer insulatingfilm 41 and then pattering the wiring material through RIE (Reactive IonEtching). Thereafter, a magnetic layer 25 is formed such that thegrowing direction of columnar grains is 30° or less from the normal-linedirection of sidewalls of the write wiring as shown in FIG. 13A by usinga plating method for plating and growing NiFe directly on the bit line22.

When forming the bit line 22 by using Cu, because the electricresistance of Cu is small, it is possible to cover a magnetic layerhaving a small film-thickness distribution in a wafer with a diameter of8 inches and as a result, a memory-chip fabrication yield can be greatlyimproved.

According to methods of the fifth and sixth embodiments, it is possibleto form a magnetic layer (NiFe or the like) obtained through a platingmethod using NiFe or Cu for a plated seed layer such as a magnetic layer(NiFe or the like) having a structure in which the growing direction ofcolumnar grains is 30° or less from the normal-line direction ofsidewalls, a structure in which grains are deposited like a layer, or astructure in which grains are amorphously deposited as shown in FIG. 12.A magnetic layer (NiFe or the like) obtained through a plating methodshows a preferable write characteristic under a comparatively-wideprocess condition.

For each of the above embodiments, a case has been described in whichthe number of recording layers of the MTJ device is 1. However, each ofthe above embodiments can be also applied to a case in which therecording layer of the MTJ device is constituted by a multilayerstructure.

The MRAM according to the first and second embodiments of the MRAM ofthe invention may be applied in various examples. Some of the applicableexamples are explained below.

APPLICABLE EXAMPLE 1

As one of applicable examples of the MRAM, FIG. 22 shows a digitalsubscriber line (DSL) data path portion of a digital subscriber line(DSL) modem. This modem includes a programmable digital signal processor(DSP) 151, an analog-to-digital converter (A/D) and digital-to-analogconverter (D/A) 152, a transmission driver 153, and a receiver amplifier154. In FIG. 22, the band pass filter is omitted, and an MRAM 155 and anEEPROM 156 are shown instead as an optional memory of various typescapable of holding a line code program.

In this example, as the memory for holding the line code program, twomemories MRAM and EEPROM are used, but the EEPROM may be replaced by theMRAM, that is, without using two memories, only the MRAM may be used.

APPLICABLE EXAMPLE 2

As another applicable example of the MRAM, FIG. 23 shows a portion forrealizing communication function in a cellphone terminal 300. As shownin FIG. 23, the portion for realizing the communication functioncomprises a transmission and reception antenna 201, an antenna duplexer202, a receiver 203, a base band processor 204, a digital signalprocessor (DSP) 205 used as audio codec, a loudspeaker 206, a microphone207, a transmitter 208, and a frequency synthesizer 209.

Also as shown in FIG. 23, the cellphone terminal 300 has a controller200 for controlling the parts of the cellphone terminal. The controller200 is a microcomputer composed by connecting a CPU 221, a ROM 222, anMRAM 223, and a flash memory 224 by way of a CPU bus 225.

Herein, the ROM 222 preliminarily stores programs to be executed in theCPU 221, and necessary data such as display font. The MRAM 223 is mainlyused as a working region, and specifically it is used when storingnecessary data in the midst of calculation as required during programexecution by the CPU 221, or when temporarily storing data to be used incommunications between the controller 200 and other parts. The flashmemory 224 stores the immediate preceding setting conditions or the likeeven if the power source of the cellphone terminal 300 is turned off, orstores the setting parameters when using by setting in the sameconditions when the power source is turned on again. That is, the flashmemory 224 is a nonvolatile memory holding the stored data even if thepower source of the cellphone terminal is turned off.

In this example, the ROM 222, MRAM 223, and flash memory 224 are used,but the flash memory 224 may be replaced by the MRAM, or the ROM 222 maybe also replaced by the MRAM.

In FIG. 23, reference numeral 211 is an audio data reproductionprocessor, 212 is an external terminal connected to the audio datareproduction processor 211, 213 is an LCD controller, 214 is an LCDconnected to the LCD controller 213, 215 is a ringer, 231 is aninterface (I/F) provided between a CPU bus 225 and an external memoryslot 232, 233 is an interface (I/F) provided between the CPU bus 225 anda key operation unit 234, 235 is an interface (I/F) provided between theCPU bus 225 and an external terminal 236, and an external memory 240 isinserted into the external memory slot 232.

APPLICABLE EXAMPLE 3

FIGS. 24 to 28 show an example in which the MRAM is applied in a cardholding media contents such as smart media (MRAM card).

In a top view in FIG. 24, reference numeral 400 is an MRAM card mainbody, 401 is an MRAM chip, 402 is an opening, 403 is a shutter, and 404denotes plural external terminals. The MRAM chip 401 is contained in theMRAM card main body 400, and is exposed to outside through the opening402. While carrying the MRAM card, the MRAM chip 401 is covered with theshutter 403. The shutter 403 is made of a material having an effect ofshielding an external magnetic field, such as ceramic material. Whentransferring the data, the shutter 403 is released, and the MRAM chip401 is exposed. The external terminals 404 are for taking out thecontents data stored in the MRAM card to outside.

FIGS. 25 and 26 are a top view and a side view of a transfer device ofcard insert type for transferring data on the MRAM card. A second MRAMcard 450 used by an end user is inserted from a slit 510 in a transferdevice 500, and pushed in until stopped by a stopper 520. The stopper520 is also used as a member for positioning the first MRAM card 550 andsecond MRAM card 450. With the second MRAM card 450 disposed atspecified position, the data stored in the first MRAM card 550 istransferred into the second MRAM card 450.

FIG. 27 is a side view of a transfer device of fit-in type. As indicatedby arrow in the drawing, in this type, aiming at the stopper 520, thesecond MRAM card 450 is fitted on the first MRAM card 550. The transfermethod is same as that in the cart insert type, and explanation isomitted.

FIG. 28 is a side view of a transfer device of slide type. In the samemanner as in the CD-ROM drive or DVD drive, a receiving tray slide 560is provided in the transfer device 500, and this receiving tray slide560 slides in the horizontal direction as indicated by arrow in thedrawing. When the receiving tray slide 560 moves to the state indicatedby the broken line in the drawing, the second MRAM card 450 is put onthe receiving tray slide 560. Then, the receiving tray slide 560 conveysthe second MRAM card 450 into the inside of the transfer device 500. Thesecond MRAM card 450 is conveyed until its leading end hits against thestopper 520, and the data is transferred, same as in the card inserttype, and explanation is omitted.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1-30. (canceled)
 31. A method for manufacturing a magnetic random accessmemory having a magnetic tunnel junction device and a write wiringinducing magnetic flux to write information, the method comprising:forming an insulating film on a substrate; forming a trench in theinsulating film; depositing a magnetic body on a bottom face of thetrench; depositing magnetic layers on sidewalls of the trench byincident ionized particles from the bottom face of the trench; andembedding the write wiring in the trench.
 32. The method according toclaim 31, wherein the magnetic layer includes at least two of: astructure in which the growing direction of columnar grains is 30° orless from the normal-line direction of the sidewalls, a structure inwhich grains are deposited like a layer, and a structure in which grainsare amorphously deposited.
 33. The method according to claim 31, whereinthe write wiring serves as a write word line.
 34. The method accordingto claim 31, further comprising: disposing a layer of Ta between theinsulating film and the magnetic layers.
 35. The method according toclaim 31, wherein the magnetic body on the bottom face of the trenchcomprises a seed layer.
 36. The method according to claim 35, whereinthe seed layer includes NiFe or Cu.
 37. The method according to claim36, wherein the magnetic body is sputtered by Ar ions in the depositingthe magnetic layers.
 38. The method according to claim 31, wherein theincident ions are supplied in the depositing a magnetic body and in thedepositing the magnetic layers.
 39. The method according to claim 38,wherein the incident ions include ions of Ni, Fe, NiFe.
 40. A method formanufacturing a magnetic random access memory having a magnetic tunneljunction device and a write wiring inducing magnetic flux to writeinformation, the method comprising: forming an insulating film on asubstrate; depositing a wiring material on the insulating film andforming the write wiring by patterning the wiring material; depositing amagnetic body on next surfaces of the insulating film; and depositing amagnetic layer on the write wiring by incident ionized particles fromthe magnetic body.
 41. The method according to claim 40, wherein themagnetic layer includes at least two of: a structure in which thegrowing direction of columnar grains is 30° or less from the normal-linedirection of the sidewalls of the write wiring, a structure in whichgrains are deposited like a layer, and a structure in which grains areamorphously deposited.
 42. The method according to claim 40, wherein thewrite wiring serves as a bit line.
 43. The method according to claim 40,wherein the magnetic body comprises a seed layer.
 44. The methodaccording to claim 43, wherein the seed layer includes NiFe or Cu. 45.The method according to claim 43, wherein the magnetic body is sputteredby Ar in the depositing the magnetic layers.
 46. The method according toclaim 40, wherein the incident ionized particles are supplied in thedepositing the magnetic body and in the depositing the magnetic layers.47. A method for manufacturing a magnetic random access memory having amagnetic tunnel junction device and a write wiring inducing magneticflux to write information, the method comprising: forming an insulatingfilm on a substrate; depositing a wiring material containing Cu on theinsulating film and forming the write wiring by patterning the wiringmaterial; and growing a magnetic layer on the write wiring through aplating method, wherein the magnetic layer has at least one of: astructure in which a growing direction of columnar grains is 30° or lessfrom the normal-line direction of sidewalls of the write wiring, and astructure in which grains are deposited like a layer, and a structure inwhich grains are amorphously deposited.
 48. The method according toclaim 47, wherein the write wiring serves as a bit line.
 49. The methodaccording to claim 31, wherein the write wiring includes Cu.